Applicant claims priority of Japanese patent application, Ser. No. 2001-367375, filed Nov. 30, 2001.
The present invention relates to a carburetor, and more particularly to a diaphragm-type carburetor that provides a fuel and air mixture to an engine.
Diaphragm-type carburetors are commonly used to supply a fuel and air mixture to an engine in accordance with engine demand. Such carburetors use a diaphragm to control at least in part the flow of liquid fuel in the carburetor in response to a signal applied to the diaphragm.
The presence of air and fuel vapor in the carburetor can inhibit liquid fuel flow in the carburetor. This can make it difficult to start an engine, and even after the engine is started, can cause unstable engine operation if the fuel vapor is not purged quickly. Air and fuel vapor can become present in the carburetor, for example, when an engine is not operated for a long period of time, or a hot engine is left out in hot ambient conditions.
A diaphragm-type carburetor has a body defining at least in part an air intake passage, a fuel metering chamber that receives fuel for delivery into the air intake passage, a fuel supply passage communicating a supply of fuel with the fuel metering chamber, and a bypass passage communicating the fuel supply passage with the air intake passage to facilitate removal of air and fuel vapor from the carburetor. The bypass passage is routed around, and does not communicate directly with the fuel metering chamber. Fuel vapor or air in the carburetor is quickly led from the bypass passage to the air intake passage to prevent a large quantity or volume of fuel vapor or air from staying in or flowing to the fuel metering chamber and thereby adversely affecting the operation of the carburetor. The present invention may be used in carburetors of substantially any type including without limitation those having piston, rotary, butterfly, barrel or slide type throttle valves.